Example in documentation doesn't seem to work

[catsclaw]

The following comes from the README file for json_serializable:

import 'package:json_annotation/json_annotation.dart';

part 't.g.dart';

@JsonSerializable()
class Sample1 {
  Sample1(this.value);

  factory Sample1.fromJson(Map<String, dynamic> json) => _$Sample1FromJson(json);

  // Sample2 is NOT annotated with @JsonSerializable(), but that's okay
  // The class has a `fromJson` constructor and a `toJson` method, which is
  // all that is required.
  final Sample2 value;

  Map<String, dynamic> toJson() => _$Sample1ToJson(this);
}

class Sample2 {
  Sample2(this.value);

  // The convention is for `fromJson` to take a single parameter of type
  // `Map<String, dynamic>` but any JSON-compatible type is allowed.
  factory Sample2.fromJson(int value) => Sample2(value);
  final int value;

  // The convention is for `toJson` to take return a type of
  // `Map<String, dynamic>` but any JSON-compatible type is allowed.
  int toJson() => value;
}

If I run dart run build_runner build on this code, it generates the following:

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 't.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Sample1 _$Sample1FromJson(Map<String, dynamic> json) =>
    Sample1(Sample2.fromJson((json['value'] as num).toInt()));

Map<String, dynamic> _$Sample1ToJson(Sample1 instance) => <String, dynamic>{
  'value': instance.value,
};

The generated code is wrong—it never calls .toJson on the Sample2 instance.